Dram and method of making

ABSTRACT

Embodiments of the present disclosure generally relate to a storage device. More specifically, embodiments described herein generally relate to a dynamic random-access memory and the method of making thereof. In one embodiment, a cell array includes at least an active region and a field region adjacent to the active region. The active region includes at least one trench, a dielectric layer disposed in the trench, a first conformal layer disposed on the dielectric layer, and a conductive material disposed on the first conformal layer. The field region includes a trench, a dielectric layer disposed in the trench, a second conformal layer disposed on the dielectric layer, and a conductive material disposed on the second conformal layer. The second conformal layer has a different composition than the first conformal layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Indian Provisional PatentApplication No. 201841042056, filed on Nov. 7, 2018, which herein isincorporated by reference.

BACKGROUND Field

Embodiments of the present disclosure generally relate to a storagedevice. More specifically, embodiments described herein generally relateto a dynamic random-access memory and the method of making thereof.

Description of the Related Art

With advances in computing technology, computing devices are smaller andhave increased processing power. Accordingly, increased storage andmemory is needed to meet the devices' programming and computing needs.The shrinking size of the devices with increased storage capacity isachieved by increase the number of storage units that having smallergeometries.

With the latest generation of increased density of storage cells,intermittent failure has appeared in some devices. Researchers havetraced the failures to repeated access to a single row of memory cellswithin the refresh window of the memory cell. For example, for a 32nanometer (nm) process, the physical adjacent word line (WL) to theaccess row has a very high probability of experiencing data corruption.The issue has been labeled as a row hammer failure by the DRAM industry.

The row hammer failure can cause charge migration across the passgate(PG) in the field region to bit line contact through the active regionby the repeated access to one row, causing data corruption in anon-accessed physically adjacent row. This condition leads to data bitfailure.

Accordingly, an improved DRAM and method for forming the DRAM areneeded.

SUMMARY

Embodiments of the present disclosure generally relate to a storagedevice. More specifically, embodiments described herein generally relateto a dynamic random-access memory (DRAM) and the method of makingthereof. In one embodiment, a cell array includes one or more firsttrenches located in an active region, a first dielectric layer disposedin the one or more first trenches, a first conformal layer disposed onthe first dielectric layer, a first conductive material disposed on thefirst conformal layer, one or more second trenches located in a fieldregion, a second dielectric layer disposed in the one or more secondtrenches, a second conformal layer disposed on the second dielectric,the second conformal layer having a different composition than the firstconformal layer, and a second conductive material disposed on the secondconformal layer.

In another embodiment, a method includes depositing a dielectric layerin a first plurality of trenches, the first plurality of trenchesincluding a second plurality of trenches in active regions and a thirdplurality of trenches in field regions, depositing a first conformallayer on the dielectric layer, depositing a mask on the second pluralityof trenches, the third plurality of trenches being exposed, removing thefirst conformal layer disposed in the third plurality of trenches,depositing a second conformal layer on the dielectric layer in the thirdplurality of trenches, removing the mask, and depositing a conductivematerial in the first plurality of trenches.

In another embodiment, a method includes depositing a dielectric layerin a first plurality of trenches, the first plurality of trenchesincluding a second plurality of trenches in active regions and a thirdplurality of trenches in field regions, depositing a first conformallayer on the dielectric layer, depositing a mask on the second pluralityof trenches, the third plurality of trenches being exposed, doping thefirst conformal layer in the third plurality of trenches to form asecond conformal layer in the third plurality of trenches, removing themask, and depositing a conductive material in the first plurality oftrenches.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlyexemplary embodiments and are therefore not to be considered limiting ofits scope, and may admit to other equally effective embodiments.

FIG. 1A is a perspective view of a cell array of a DRAM.

FIG. 1B is a top view of the cell array of FIG. 1A.

FIG. 2 is a flow diagram of a method for forming the cell array of FIG.1A.

FIGS. 3A-3G illustrate schematic cross-sectional views of a portion ofthe cell array of FIG. 1A during different stages of the method of FIG.2.

FIG. 4 is a flow diagram of a method for forming the cell array of FIG.1A.

FIGS. 5A-5F illustrate schematic cross-sectional views of a portion ofthe cell array of FIG. 1A during different stages of the method of FIG.4.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments of the present disclosure generally relate to a storagedevice. More specifically, embodiments described herein generally relateto a dynamic random-access memory and the method of making thereof. Inone embodiment, a cell array includes at least an active region and afield region adjacent to the active region. The active region includesat least one trench, a dielectric layer disposed in the trench, a firstconformal layer disposed on the dielectric layer, and a conductivematerial disposed on the first conformal layer. The field regionincludes a trench, a dielectric layer disposed in the trench, a secondconformal layer disposed on the dielectric layer, and a conductivematerial disposed on the second conformal layer. The second conformallayer has a different composition from the first conformal layer. Thesecond conformal layer is a work function layer that reducesinterference from the neighboring active regions, leading to reduceddata bit failure.

FIG. 1A is a perspective view of a cell array 100 of a DRAM according toone embodiment described herein. Bit lines are omitted in FIG. 1A forclarity. The cell array 100 includes a plurality of active regions 102and a plurality of field regions 104. The active regions 102 and thefield regions 104 are alternately positioned. Each active region 102includes one or more trenches 106 formed in one or more semiconductormaterials 107. The semiconductor materials 107 include one or more ofsilicon, doped silicon, or other suitable semiconductor material. Eachtrench 106 includes a first portion 108 and a second portion 110. Adielectric layer 112 is disposed on the first portion 108 of the trench106. The dielectric layer 112 may be an oxide, such as silicon oxide. Aconformal layer 114 is disposed on the dielectric layer 112, and aconductive material 116 is disposed on the conformal layer 114. In oneembodiment, the conductive material 116 functions as a gate (i.e.,buried word line) and is fabricated from an electrically conductivematerial, such as a metal. In one embodiment, the conformal layer 114 isfabricated from a metal nitride.

A dielectric layer 118 is formed on the second portion 110 of the trench106. The dielectric layer 118 may be fabricated from the same materialas the dielectric layer 112. In one embodiment, the dielectric layer 118is formed on the side wall of the second portion 110 of the trench 106and on the dielectric layer 112, the conformal layer 114, and theconductive material 116. A silicon nitride layer 120 is disposed on thedielectric layer 118.

Each field region 104 includes a shallow trench isolation (STI) 122. Atrench 124 is formed in the STI 122. The trench 124 includes a firstportion 126 and a second portion 128. A dielectric layer 130 is disposedon the first portion 126 of the trench 124. The dielectric layer 130 maybe fabricated from the same material as the dielectric layer 112. Aconformal layer 132 is disposed on the dielectric layer 130, and aconductive material 134 is disposed on the conformal layer 132. In oneembodiment, the conductive material 134 is fabricated from the samematerial as the conductive material 116. The conformal layer 132 is awork function layer having a different composition than the conformallayer 114. The conformal layer 132 may be fabricated from a metal, dopedmetal nitride, or other suitable material. The conformal layer 132,which is a work function layer having a different composition than theconformal layer 114 in the active region 102, reduces interference fromthe neighboring active regions 102, leading to reduced data bit failure.

A dielectric layer 136 is formed on the second portion 128 of the trench124. The dielectric layer 136 may be fabricated from the same materialas the dielectric layer 130. In one embodiment, the dielectric layer 136is formed on the side wall of the second portion 128 of the trench 124and on the dielectric layer 130, the conformal layer 132, and theconductive material 134. A silicon nitride layer 138 is disposed on thedielectric layer 136. In one embodiment, the active regions 102 includea row of transistors (i.e., the conductive material 116 functioning asgates), and the row of transistors is separated from another row oftransistors by a dielectric material 140. In one embodiment, thedielectric material 140 is silicon nitride.

FIG. 1B is a top view of the cell array 100 of FIG. 1A according to oneembodiment described herein. As shown in FIG. 1B, the cell array 100includes a plurality of bit lines 150 disposed over the dielectric layer136, the silicon nitride layer 138, and the dielectric material 140. Thecell array 100 further includes a plurality of active regions 102 and aplurality of field regions 104. Each filed region 104 is disposedbetween two active regions 102. The region 152 in the field region 104represents the location of the trench 124 including the conformal layer132. The conformal layer 132, which is a work function layer, reducesinterference from the neighboring active regions 102, leading to reduceddata bit failure.

FIG. 2 is a flow diagram of a method 200 for forming the cell array 100of FIG. 1A. FIGS. 3A-3G illustrate schematic cross-sectional views of aportion of the cell array 100 of FIG. 1A during different stages of themethod of FIG. 2. The method 200 starts at operation 202 by depositing adielectric layer 302 in a plurality of trenches 304, 306, as shown inFIG. 3A. The trenches 304 are located in active regions 308, and thetrench 306 is located in the field region 310. The active regions 308may be the active regions 102 of the cell array 100 as shown in FIG. 1A,and the field region 310 may be the field region 104 of the cell arrayas shown in FIG. 1A. The trenches 304 may be the trenches 106 of thecell array 100 as shown in FIG. 1A, and the trench 306 may be the trench124 of the cell array 100 as shown in FIG. 1A. The dielectric layer 302may be the same as the dielectric layers 112, 118, 130, 136 of the cellarray 100 as shown in FIG. 1A. The dielectric layer 302 may be depositedby any suitable method. In one embodiment, the dielectric layer 302 is aconformal layer that is deposited by an atomic layer deposition (ALD)process.

Next, at operation 204, a first conformal layer 312 is deposited on thedielectric layer 302, as shown in FIG. 3B. The first conformal layer 312may be the conformal layer 114 of the cell array 100 as shown in FIG.1A. The first conformal layer 312 may be deposited by any suitablemethod. In one embodiment, the first conformal layer 312 is a metalnitride layer that is deposited by an ALD process. At operation 206, amask 314 is deposited on trenches 304 in the active regions 308, asshown in FIG. 3C. The mask 314 may be any suitable mask. In oneembodiment, the mask 314 is a photoresist. In one embodiment, the maskis a multi-layer structure. The mask 314 covers the trenches 304 of theactive regions 308, while the trench 306 of the field region 310 isexposed.

At operation 208, the first conformal layer 312 disposed of the trench306 in the field region 310 is removed, as shown in FIG. 3D. The removalof the first conformal layer 312 in the trench 306 may be achieved byany suitable method. In one embodiment, the removal of the firstconformal layer 312 in the trench 306 is achieved by wet etching. Next,at operation 210, a second conformal layer 320 is deposited in thetrench 306 of the field region 310, as shown in FIG. 3E. The secondconformal layer 320 may be any layer that has a different compositionthan the first conformal layer 312. The second conformal layer 320 is awork function layer. The second conformal layer 320 may be the same asthe conformal layer 132. In one embodiment, the second conformal layer320 is deposited by an ALD process.

At operation 212, the mask 314 disposed on the trenches 304 of theactive regions 308 is removed, as shown in FIG. 3F. The mask 314 may beremoved by any suitable process. In one embodiment, the mask 314 isremoved by a stripping process. Next, at operation 214, a conductivematerial 322 is deposited in the trenches 304, 306, as shown in FIG. 3G.The conductive material 322 may be the same as the conductive material116, 134 of the cell array 100 as shown in FIG. 1A. The conductivematerial 322 may be deposited by any suitable method. In one embodiment,the conductive material 322 is deposited by a chemical vapor deposition(CVD) process.

FIG. 4 is a flow diagram of a method 400 for forming the cell array 100of FIG. 1A. FIGS. 5A-5F illustrate schematic cross-sectional views of aportion of the cell array 100 of FIG. 1A during different stages of themethod of FIG. 4. The method 400 starts at operation 402 by depositing adielectric layer 502 in a plurality of trenches 504, 506, as shown inFIG. 5A. The trenches 504 are located in active regions 508, and thetrench 506 is located in the field region 510. The active regions 508may be the active regions 102 of the cell array 100 as shown in FIG. 1A,and the field region 510 may be the field region 104 of the cell arrayas shown in FIG. 1A. The trenches 504 may be the trenches 106 of thecell array 100 as shown in FIG. 1A, and the trench 506 may be the trench124 of the cell array 100 as shown in FIG. 1A. The dielectric layer 502may be the same as the dielectric layers 112, 118, 130, 136 of the cellarray 100 as shown in FIG. 1A. The dielectric layer 502 may be depositedby any suitable method. In one embodiment, the dielectric layer 502 is aconformal layer that is deposited by an ALD process.

Next, at operation 404, a first conformal layer 512 is deposited on thedielectric layer 502, as shown in FIG. 5B. The first conformal layer 512may be the conformal layer 114 of the cell array 100 as shown in FIG.1A. The first conformal layer 512 may be deposited by any suitablemethod. In one embodiment, the first conformal layer 512 is a metalnitride layer that is deposited by an ALD process. At operation 406, amask 514 is deposited on trenches 504 in the active regions 508, asshown in FIG. 5C. The mask 514 may be any suitable mask. In oneembodiment, the mask 514 is a photoresist mask. In one embodiment, themask is a multi-layer structure. The mask 514 covers the trenches 504 ofthe active regions 508, while the trench 506 of the field region 510 isexposed.

At operation 408, the first conformal layer 512 disposed of the trench506 in the field region 510 is doped with a dopant D to form a secondconformal layer 520, as shown in FIG. 5D. The dopant D may be anysuitable dopant. As a result, the first conformal layer 512 is disposedin each trench 304 of the active region 308, while the second conformallayer 520 is disposed in each trench 306 of the field region 310. Thesecond conformal layer 520 has a different composition than the firstconformal layer 512, since the second conformal layer 520 includes thedopant compared to the first conformal layer 512.

At operation 410, the mask 514 disposed on the trenches 504 of theactive regions 508 is removed, as shown in FIG. 5E. The mask 514 may beremoved by any suitable process. In one embodiment, the mask 514 isremoved by a stripping process. Next, at operation 412, a conductivematerial 522 is deposited in the trenches 504, 506, as shown in FIG. 5F.The conductive material 522 may be the same as the conductive material116, 134 of the cell array 100 as shown in FIG. 1A. The conductivematerial 522 may be deposited by any suitable method. In one embodiment,the conductive material 522 is deposited by a CVD process.

The DRAM including the cell array, such as the cell array 100, having awork function layer, such as the conformal layers 132, 320, 520,disposed in trenches of the field region reduces interference from theneighboring active regions, leading to reduced data bit failure. Thecell array may have 4F2 cell structure, 6F2 cell structure, 8F2 cellstructure, or other suitable cell structure. The cell array may beutilized in other access devices, such as FinCAT and nanowire devices.

While the foregoing is directed to embodiments of the presentdisclosure, other and further embodiments of the disclosure may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims that follow.

1. A cell array, comprising: one or more first trenches located in anactive region; a first dielectric layer disposed in the one or morefirst trenches; a first conformal layer disposed on the first dielectriclayer in the one or more first trenches; a first conductive materialdisposed on and in direct contact with the first conformal layer in theone or more first trenches; one or more second trenches located in afield region; a second dielectric layer disposed in the one or moresecond trenches; a second conformal layer disposed on the seconddielectric layer in the one or more second trenches, the secondconformal layer having a different composition than the first conformallayer; and a second conductive material disposed on and in directcontact with the second conformal layer in the one or more secondtrenches.
 2. The cell array of claim 1, wherein the first dielectriclayer is an oxide layer.
 3. The cell array of claim 2, wherein the firstconformal layer is a metal nitride layer.
 4. The cell array of claim 3,wherein the first conductive material and the second conductive materialare a metal.
 5. The cell array of claim 4, wherein the second conformallayer is a doped metal nitride layer having one or more dopants.
 6. Thecell array of claim 4, wherein the second conformal layer comprises ametal.
 7. The cell array of claim 1, wherein the first conformal layeris a metal nitride layer.
 8. The cell array of claim 7, wherein thesecond conformal layer comprises a metal.
 9. A method, comprising:depositing a dielectric layer in a first plurality of trenches, thefirst plurality of trenches comprising a second plurality of trenches inactive regions and a third plurality of trenches in field regions;depositing a first conformal layer on the dielectric layer; depositing amask on the second plurality of trenches, the third plurality oftrenches being exposed; removing the first conformal layer disposed inthe third plurality of trenches; depositing a second conformal layer onthe dielectric layer in the third plurality of trenches; removing themask; and depositing a conductive material in the first plurality oftrenches.
 10. The method of claim 9, wherein the dielectric layer is anoxide layer.
 11. The method of claim 10, wherein the first conformallayer is a metal nitride layer.
 12. The method of claim 11, wherein theconductive material is a metal.
 13. The method of claim 12, wherein thesecond conformal layer comprises a metal.
 14. The method of claim 9,wherein the second conformal layer comprises a metal.
 15. A method,comprising: depositing a dielectric layer in a first plurality oftrenches, the first plurality of trenches comprising a second pluralityof trenches in active regions and a third plurality of trenches in fieldregions; depositing a first conformal layer on the dielectric layer;depositing a mask on the second plurality of trenches, the thirdplurality of trenches being exposed; doping the first conformal layer inthe third plurality of trenches to form a second conformal layer in thethird plurality of trenches; removing the mask; and depositing aconductive material in the first plurality of trenches.
 16. The methodof claim 15, wherein the dielectric layer is an oxide layer.
 17. Themethod of claim 16, wherein the first conformal layer is a metal nitridelayer.
 18. The method of claim 17, wherein the conductive material is ametal.
 19. The method of claim 15, wherein the second conformal layer isa doped metal nitride layer having one or more dopants.
 20. The methodof claim 19, wherein the first conformal layer is a metal nitride layer.